1. Field of the Invention
The present invention relates to an ultra-wideband transmitter and receiver, and an ultra-wideband wireless communicating method using ultra-wideband.
2. Description of the Related Art
An ultra-wideband wireless communication system has been developed as a new type of data communication system in a spread spectrum communication system. The ultra-wideband wireless communication system performs data communication by spreading data to ultra wide frequency band of about 1 GHz and overlapping the spread data with a pulse without using a carrier wave. Because data transmitted with each frequency band has only intensity of noise magnitude in the ultra-wideband wireless communication system, wireless devices using the same frequency band interfere with each other and power consumption is low.
Ultra-wideband wireless communication system uses a repeated code, which transmits a predetermined number of impulses with respect to each bit. FIG. 32 illustrates an example of a time format of a signal exchange in the conventional ultra-wideband wireless transceiver. Time axis is divided into a plurality of sections in such a manner that it has one section for every time period T. Reference time is shown by a dotted line in FIG. 32. The conventional ultra-wideband wireless transceiver transmits respective pulses generated at intervals of pseudo random times T1, T2, T3, and T4 from the reference time.
FIG. 33 is an enlarged view of a pulse generated at an interval of the pseudo random time T1 from the reference time. When a transmitter transmits data 1, it transmits a pulse at pseudo random time T1. When the transmitter transmits data 0, it transmits the pulse at time T1+TS. TS is a previously determined time.
FIG. 34 illustrates a relationship between data and a signal waveform. As illustrated in FIG. 34, when a receiver receives a pulse generated at an interval of the pseudo random time T1 from the reference time, it demodulates data 1. When the receiver receives a pulse generated at an interval of time T1+TS from the reference time, it demodulates data 0.
FIG. 35 is a block diagram showing a configuration of a demodulating circuit, which performs a data demodulation in a receiver. FIG. 36 is a view illustrating a waveform of a reference signal. The demodulating circuit generates the reference signal illustrated in FIG. 36 at a predetermined time. That is, the demodulating circuit generates a positive pulse at time T1 and generates a negative pulse at time TS. A multiplier of the demodulating circuit multiplies a received signal by the reference signal.
FIG. 37 is a waveform illustrating a multiplication result signal of the received signal and the reference signal when the demodulating circuit demodulates data 1. As illustrated in FIG. 37, when a positive pulse is generated, the demodulating circuit demodulates data 1.
FIG. 38 is a waveform illustrating a multiplication result signal of the received signal and the reference signal when the demodulating circuit demodulates data 0. As illustrated in FIG. 38, when a negative pulse is generated, the demodulating circuit demodulates data 0. Generally, when performing a data communication while adding a signal to only an impulse having logic 1, because the pulse is affected by a noise, reliance of data is reduced. In order to prevent that, a plurality of pulses are added thereto.
FIG. 39 is a view illustrating a configuration of a receiver when a plurality of pulses are added. A transmitter transmits a pulse at pseudo random times T1, T2, T3, and T4 illustrated in FIG. 39.
FIG. 40 is a view illustrating a waveform of a reference signal. A receiver multiplies a received signal by the reference signal illustrated in FIG. 40 using the reference signal and outputs a multiplied result signal. An adder accumulates the multiplied result signal from the receiver and outputs it to a determining section.
FIG. 41 is a view illustrating a time change of an output value when data is data 1. When the data is data 1, when time lapses, because an adder sequentially adds the multiplied results to a reference signal at time periods T1, T2, T3, and T4, the outputs are increased.
FIG. 42 is a view illustrating a time change of an output value when data is data 0. When the data is data 0, when time lapses, because the adder sequentially adds the multiplied results to the reference signal at time periods T1, T2, T3, and T4, the outputs are reduced. An average of the outputs is compared with a threshold value and data is determined according to the compared result.
According to the above-described operation, a demodulation of data is performed.
When determining a signal using the conventional ultra-wideband wireless communication system, following problems occur. First, a transmitter needs to generate exact pseudo random times of T1, T2, T3, and T4. For example, when a clock period of 5 GHz is used, a counter of a digital circuit operating at 5 GHz is required. Operating the counter increases power consumption.
When the transmitter generates the signal at an exact time, the receiver needs to exactly estimate a time format by any method in order to prevent a wave performance from being deteriorated. The deterioration of the wave performance occurs due to a bad estimation of the signal format having a period T. Furthermore, the conventional ultra-wideband wireless communication system cannot eliminate multi-pass.
FIG. 43 is a view illustrating a transmitting status of signals when a multiple pass occurs. When a transmitter transmits two signals to a receiver through two wave paths, a delay difference Td occurs between two signals due to a difference of the two wave paths. For example, when a delay time Td between a directly received signal and a signal reflected and received from an object such as an interior wall is 0.2 nsec, a difference of wave paths is 6 cm. In a closed space such as an interior of a room, a multiple pass frequently occurs due to a difference of wave paths.
FIG. 44 is a view illustrating a received signal when a multi-pass occurs in data 1, and FIG. 45 is a view illustrating an output of a multiplier when a multi-pass occurs. As illustrated in FIG. 45, a multiplier multiplies the received signal by the reference signal, because areas of positive and negative values of the multiplied result signal are identical with each other, an output of the adder becomes zero. For this reason, it is incorrectly determined that there is no data, and data 1 cannot be demodulated.